#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

int main4()
{
	int i,j;
	int x = 0;
	int y = 0;

	int velocity_x = 1;
	int velocity_y = 1;
	int left = 0;
	int right = 20;
	int top  = 0;
	int bottom = 10;

	while(1)
	{
		x = x + velocity_x;
		y = y + velocity_y;

		system("cls");

		for(i = 0; i < x; i++)
		{
			printf("\n");
		}
		for(j = 0; j < y; j++)
		{
			printf(" ");
		}
		printf("O");
		printf("\n");
		Sleep(20);

		if((x == top) || (x == bottom))
			velocity_x = -velocity_x;
		if((y == left) || (y == right))
			velocity_y = -velocity_y;
	}
	return 0;
}